Geologica Acta, Vol.9, Nº 1, March 2011, 1-12 DOI: 10.1344/105.000001648 Available online at www.geologica-acta.com A new sauropod titanosaur from the Plottier Formation (Upper Cretaceous) of Patagonia (Argentina) 1 2 3 4 3 3 3 L.S. FILIPPI J.I. CANUDO J.L. SALGADO A. GARRIDO R. GARCÍA I. CERDA A. OTERO 1 Museo Municipal “Argentino Urquiza” Jujuy y Chaco s/n, 8319 Rincón de los Sauces, Neuquén, Argentina. E-mail: [email protected] 2 Grupo Aragosaurus - IUCA (www.aragosaurus.com), Paleontología, Facultad de Ciencias, Universidad de Zaragoza Pedro Cerbuna 12, 50009 Zaragoza, Spain. E-mail: [email protected] 3 CONICET-INIBIOMA, Museo de Geología y Paleontología, Universidad Nacional del Comahue Buenos Aires 1400, 8300 Neuquén, Argentina. Salgado E-mail: [email protected] García E-mail: [email protected] Cerda E-mail: [email protected] Otero E-mail: [email protected] 4 Museo Provincial de Ciencias Naturales “Prof. Dr. Juan Olsacher” Dirección Provincial de Minería, Etcheluz y Ejército Argentino, 8340 Zapala, Neuquén, Argentina. E-mail: [email protected] ABSTRACT This paper presents a new titanosaur sauropod, collected from levels of reddish clays assigned to the Plottier Formation (Coniacian-Santonian). The holotype of Petrobrasaurus puestohernandezi gen. et. sp. nov. is a disarticulated specimen, from which teeth, cervical, dorsal and caudal vertebrae, sternal plates, metacarpals, femora, tibia, a fragment of ilium, pubis, haemal arches, and cervical and dorsal ribs have been preserved. This period is of particular interest because it saw the definitive isolation of the vertebrate faunas of Patagonia, with the separation of South America from the rest of Gondwana, a process that had begun during the Early Cretaceous. Although some of the characters observed in Petrobrasaurus gen. nov. suggest a relationship with the South American clade Lognkosauria, this new sauropod is regarded as Titanosauria incertae sedis until a more profound analysis of the Titanosauria that in which it is included is undertaken. KEYWORDS Titanosauria. Plottier Formation. Coniacian-Santonian. Late Cretaceous. Río Neuquén Subgroup. Argentina. INTRODUCTION tetrapods that lived on either side of the incipient South Atlantic (Gasparini et al., 2007). The question of when the The separation of South America from the rest of definitive separation of Africa and South America actually Gondwana at the end of the Early Cretaceous produced a took place raises certain doubts, since the traditional gradual evolutionary differentiation among the groups of model, which posits the separation of the two continents in 1 L.S. FILIPPI et al. A new sauropod titanosaur from Plottier Formation the Early Cretaceous (Sampson et al., 1998), encounters The quarry where the remains were found was produced problems with the dinosaur record. On the basis of the by land-levelling operations prior to the installation of the presence of abelisauroid theropods in Africa, Sereno et PH 1597 oil well by the Petrobras oil company. During al. (2004) propose that the connection was operative the course of the autumn of 2006 and the spring of 2007, at least until 95 million years ago (Cenomanian) and excavation work was carried out as part of a cooperative could have persisted intermittently until the Coniacian. project between the Museum of Rincón de los Sauces, the Upchurch (2008), on the other hand, developed a new Universidad El Comahue (Argentina) and the Universidad model of Gondwanan fragmentation and re-connection, de Zaragoza (Spain). The objective of this paper is to according to which the isolation of Africa would have describe this specimen of sauropod and to discuss its started some 100 million years ago. The best way of phylogenetic position and its palaeobiogeographical contributing new arguments to this discussion is by implications. providing new evidence of dinosaurs of the Cenomanian- Turonian and establishing what their phylogenetic relations are. Studies of the Late Turonian/Coniacian dinosaurs of GEOLOGICAL SETTING. STRATIGRAPHY South America are particularly significant in assessing the time and the manner of this differentiation. Leanza et al. The fossils were excavated in the vicinity of the PH (2004) proposed a specific term to distinguish a particular 1597 oil well, within the Puesto Hernández production faunal association for the Late Turonian/ Coniacian, the field. The well is located 25km to the north-west of the city ‘Neuquenian Tetrapod’ association in the specific case of of Rincón de los Sauces, in the north of the province of the Neuquén Basin. Neuquén, Patagonia, Argentina (Fig. 1). In stratigraphic terms, the Neuquenian is located The quarry is located in the mid-high part of the Plottier in the Río Neuquén Subgroup, which is divided into Formation (Fig. 2), dated by Musacchio and Vallati (2007) the Portezuelo and Plottier Formations (Ramos, 1981; on the basis of their non-marine microfossil assemblage Leanza et al., 2004). In recent years, the Portezuelo to the Coniacian-Santonian interval. This unit is composed Formation has yielded important vertebrate remains of alternating whitish quartzite sandstones and reddish such as Patagonykus puertai Novas 1996, Megaraptor mudstones. The sandstone levels are made up of normal- namunhuaiquii Novas 1998, Neuquenraptor argentinus grading deposits disposed in amalgamated channelized Novas and Pol, 2005. The Neuquenian is characterized by a singular fauna (Gasparini et al., 2007), marked by the apparent extinction of rebbachisaurid sauropods and the presence of large-sized titanosaurs such as Futalognkosaurus dukei Calvo et al., 2007a, and of theropods including putative basal tetanurans such as Megaraptor, unenlagines (Bonaparte, 1999) and alvaresaurids (Novas, 1997). The outcrops of the Río Neuquén Subgroup, around the city of Rincón de los Sauces, have proved to be especially prolific in the discovery of sauropods like Rinconsaurus caudamirus Calvo and González-Riga, 2003, and Muyelensaurus pecheni Calvo et al., 2007b. Also, in the nearby province of Mendoza, Mendozasaurus neguyelap González-Riga, 2003, and Malarguesaurus florenciae González-Riga et al., 2009 has been collected. By contrast, the dinosaur fossil record of the Plottier Formation (from the late part of the Coniacian to the early part of the Santonian; Legarreta and Gulisano, 1989; Cruz et al., 1989) is very sparse, being limited to remains of a large coelurosaur theropod and fragmentary remains of titanosaur sauropods, assigned to cf. Antarctosaurus giganteus (see the references in Leanza et al., 2004, and Gasparini et al., 2007). Here we describe a new species of titanosaur sauropod recovered from the Plottier Formation FIGURE 1 Location Map of Puesto Hernández (Neuquén, Patagonia, at Rincón de los Sauces (Fig. 1). Argentina). Geologica Acta, 9(1), 1-12 (2011) 2 DOI: 10.1344/105.000001648 L.S. FILIPPI et al. A new sauropod titanosaur from Plottier Formation bodies, showing a predominance of downstream accretion spinoprezygapophyseal lamina, tp: transverse process, tu: and sandy bedform architectural element types (sensu tuberculum, ulc: ulnar condyle. Miall, 1996). These sediments are interpreted as fluvial deposits belonging to sandy braided channel systems. The fossil-bearing levels comprise ruddy brown mudstones approximately three metres thick, characterized by a high sand content microconglomerate-sized heterometric detrital grains of a siliceous and carbonate nature. The fossil remains of the sauropod were found at the base of this level, there being no other fossil vertebrates in the rest of the level (Fig. 2). The detritus is irregularly distributed in the form of carbonate nodules of a possibly pedogenic origin, as well as small transported cylindrical galleries of invertebrates, which are not found ‘in situ’. Small logs and plant debris are also frequent components within this level. The sauropod bones were found to be associated and disarticulated, but respecting approximately the original position within the skeleton. The long bones and the vertebrae were complete and without any taphonomic breaks, whereas some of the ribs were fragmented and the teeth of the sauropod were isolated. The bones do not show signs of transport such as abrasion or erosion. This indicates that the transport of the bony remains was minor and restricted to a small area. The sedimentological characteristics of the fossiliferous level suggest a deposition mechanism linked to a dense muddy flow. The remains were scattered over an area of 60m² and with no repeated pieces, suggesting they belong to a single specimen. Five isolated theropod tooth crowns were associated with the sauropod bones. We interpreted these as being the result of scavengers feeding on the carcass of the sauropod, since there are no signs of transport (Canudo et al., 2009b). Institutional Abbreviations: MAU-Pv-PH: Museo Argentino Urquiza – Paleontología de Vertebrados – Puesto Hernández. Anatomical Nomenclature: acpl: anterior centropa- rapophyseal lamina, apcdl: accessory posterior centro- diapophyseal lamina, cap: capitulum; cc: cnemial crest, cpol: centropostzygapophyseal lamina, dp: diapophysis, dpc: deltopectoral crest, f: small fossae, fa: articular facet, fi: interzygapophyseal fossa, fp: pubic foramen, ft: fourth trochanter, hd: articular head, ilped: iliac peduncle, lb: lateral bulge, nc: neural canal, ns: neural spine, pcdl: posterior centrodiapophyseal lamina, pcpl: posterior centroparapophyseal lamina, pl: pleurocoel, pn c: pneumatic cavity,